Peroxidase-Catalyzed Oxidation of Protein Sulfhydryls Mediated by Iodine

Edwin Thomas, Thomas M. Aune

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Lactoperoxidase, myeloperoxidase, or horseradish peroxidase catalyzed the peroxide-dependent oxidation of protein sulfhydryls in the presence of iodide. Sulfhydryl oxidation was mediated by the oxidation of iodide to iodine. About 1 mol of sulfhydryls of bovine serum albumin or β-lactoglobulin was oxidized per mol of peroxide or iodine. Sulfhydryls were oxidized to the sulfenyl iodide derivative as indicated by the loss of iodide from solution and formation of a derivative that reacted with the sulfenyl-specific reagent, 4,4′-bis(dimethylamino) thiobenzophenone (thio-Michler's ketone). Peroxidase-catalyzed oxidation of sulfhydryls was proportional to peroxide and independent of iodide concentration over a wide range. Therefore, each iodide ion could participate in the oxidation of a number of sulfhydryls. At low iodide concentrations, the yield of sulfenyl derivatives also exceeded the amount of iodide. These results indicated that sulfenyl iodide was in equilibrium with sulfenic acid and free iodide ion. At low iodide concentrations, release of iodide from sulfenyl iodide permitted reoxidation of iodide to iodine. When the initial sodium iodide concentration was less than 1 μM, no sulfhydryl oxidation was detected regardless of peroxide or peroxidase concentrations. Also, over a narrow range of iodide concentrations, sulfhydryl oxidation was not proportional to peroxide. Under these conditions, depletion of iodide and competition by electron donors other than iodide appeared to limit iodine formation. Although a lower limit for iodide turnover was observed, only small amounts of iodide were required for oxidation of large amounts of protein sulfhydryls. Therefore, in comparing the effects of iodine with those of the peroxidase system, the valid quantitative comparison can be between iodine and peroxide concentrations, rather than between iodine and iodide concentrations.

Original languageEnglish (US)
Pages (from-to)3581-3586
Number of pages6
JournalBiochemistry
Volume16
Issue number16
DOIs
StatePublished - Aug 1 1977
Externally publishedYes

Fingerprint

Iodides
Iodine
Peroxidase
Oxidation
Proteins
Peroxides
Derivatives
Sulfenic Acids
Ions
Sodium Iodide
Lactoperoxidase
Lactoglobulins

All Science Journal Classification (ASJC) codes

  • Biochemistry

Cite this

Peroxidase-Catalyzed Oxidation of Protein Sulfhydryls Mediated by Iodine. / Thomas, Edwin; Aune, Thomas M.

In: Biochemistry, Vol. 16, No. 16, 01.08.1977, p. 3581-3586.

Research output: Contribution to journalArticle

Thomas, Edwin ; Aune, Thomas M. / Peroxidase-Catalyzed Oxidation of Protein Sulfhydryls Mediated by Iodine. In: Biochemistry. 1977 ; Vol. 16, No. 16. pp. 3581-3586.
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AB - Lactoperoxidase, myeloperoxidase, or horseradish peroxidase catalyzed the peroxide-dependent oxidation of protein sulfhydryls in the presence of iodide. Sulfhydryl oxidation was mediated by the oxidation of iodide to iodine. About 1 mol of sulfhydryls of bovine serum albumin or β-lactoglobulin was oxidized per mol of peroxide or iodine. Sulfhydryls were oxidized to the sulfenyl iodide derivative as indicated by the loss of iodide from solution and formation of a derivative that reacted with the sulfenyl-specific reagent, 4,4′-bis(dimethylamino) thiobenzophenone (thio-Michler's ketone). Peroxidase-catalyzed oxidation of sulfhydryls was proportional to peroxide and independent of iodide concentration over a wide range. Therefore, each iodide ion could participate in the oxidation of a number of sulfhydryls. At low iodide concentrations, the yield of sulfenyl derivatives also exceeded the amount of iodide. These results indicated that sulfenyl iodide was in equilibrium with sulfenic acid and free iodide ion. At low iodide concentrations, release of iodide from sulfenyl iodide permitted reoxidation of iodide to iodine. When the initial sodium iodide concentration was less than 1 μM, no sulfhydryl oxidation was detected regardless of peroxide or peroxidase concentrations. Also, over a narrow range of iodide concentrations, sulfhydryl oxidation was not proportional to peroxide. Under these conditions, depletion of iodide and competition by electron donors other than iodide appeared to limit iodine formation. Although a lower limit for iodide turnover was observed, only small amounts of iodide were required for oxidation of large amounts of protein sulfhydryls. Therefore, in comparing the effects of iodine with those of the peroxidase system, the valid quantitative comparison can be between iodine and peroxide concentrations, rather than between iodine and iodide concentrations.

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